Diabetologia 13, 281-284 (1977) Diabetologia by Springer-Verlag 1977 Incidence, Seasonal and Geographical Patterns of Juvenile-Onset Insulin-Dependent Diabetes Mellitus in Denmark B. Christau a, H. Kromann 1, O. Ortved Andersen2, M. Christy 1, K. Buschard 3, K. Arnung4, I. Hojland Kristensen5, B. Peitersen6, J. Steinrud5, and J. Nerup 1 1Steno Memorial Hospital, Gentofte, 2Medical Department E, Frederiksberg Hospital, Copenhagen, 3Medical Department, Hvidovre Hospital, Hvidovre, 4Medical Department F, Herlev Hospital, Herlev, 5Departments of Medicine and Pediatrics, Frederiksborg County Hospital, Hillerod, and 6Children's Hospital, Fuglebakken, Copenhagen, Denmark The study was based on two assumptions. First Summary. The incidence, sex, seasonal and geo- that every patient with newly diagnosed juvenile-on- graphical patterns of juvenile-onset insulin-depen- set insulin-dependent diabetes mellitus (j. i. d. m.) dent diabetes mellitus (j. i. d. m.) were studied re- aged 0-29 years and diagnosed between January 1, trospectively on one third of the Danish population 1970 and December 31, 1974 was referred to a hos- 1970-1974. The j. i. d. m. incidence remained fairly pital, and secondly that the referrals would be made constant during the study period, the average being to the in- or outpatient services of the paediatric and 13.2 per 100000 per year. The total number of boys medical departments. exceeded the number of gifts by 27 per cent. A The survey area comprised the city of Copenha- marked peak of incidence was found at 12-14 years, gen, the County of Copenhagen (suburban in earlier for females than for males. A seasonal varia- character) and the County of Frederiksborg (partly tion in onset (diagnosis) of j. i. d. m. was observed rural and partly suburban in character). The area with the lowest number of new cases in May-July. covers 1961 square kilometers (4.5 per cent of the The j.i.d,m, incidence seemed to show socio- Danish territory1) and contains a population of economic differences, being highest in those parts 1598754 (average of 1970-74) or 32 per cent of of the survey area with lower status. the total Danish population. The age group 0-29 years in the survey area comprised 716285 persons Key words: Incidence, seasonal variation, geo- or 30.8 per cent of the total Danish population in graphical pattern, sex-difference, epidemiology, this age group. juvenile-onset, insulin-dependent, diabetes mellitus. All hospital records of newly diagnosed insulin- dependent diabetics aged less than 30 at the time of diagnosis were collected. Name, date of birth, sex, Solidly ascertained incidence data on juvenile-onset date of diagnosis, and place of residence at diagnosis diabetes mellitus are sparse. Bloom and co-workers were noted for each patient. This sample of 474 pa- [1] reported an incidence of 7.67 per 100000 per tients comprised the analysed group of diabetics. year in the U. K. in 1975 and described the influ- The validity of the above-mentioned assumptions ence of age, sex and seasonal variation on the inci- was checked by a questionnaire to the general prac- dence. tioners and the few specialists in private practice in The present study was tmdertaken in order to the survey area. Official Danish statistical yearbooks produce comparable data from Denmark. were used as sources of data for calculations of the age-corrected incidences. Material and Methods Results Denmark is well suited for epidemiological studies The ascertainment was almost complete, since only due to an ethnically uniform Caucasian, non-migrat- five patients diagnosed in the survey period were ing cooperative population, a public health care sys- tem and an effective national register. 1 Greenland and The Faroe Islands excluded 282 B. Christau et al.: Incidence of Juvenile-Onset Diabetes Mellitus Table 1. The number of juvenile-onset insulin-dependent diabe- Table 2. Age corrected incidence (annual number per 100000) of tics aged 0-29 years, diagnosed in the survey area 1970-74 j. i. d. m. for age groups 0-29 years, 0--14 years and 15-29 years YEAR I MALE FEMALE TOTAL AGE GROUP MALE FEMALE TOTAL 1970 46 51 97 ANNUAL 0 - 14 15.0 13.2. 13.7 1971 54 34 88 NUMBER 15 -- 29 14.3 10.8 12,8 1972 62 36 98 PER 100000 0 - 29 14.5 11.9 13.2 1973 43 48 91 1974 60 40 100 1970--1974 265 209 474 ANNUAL NUMBER PER NUMBER 100.000 OF CASES 25 20 15 \.. .4 ;, ',x o~ ../ I -~ % \ ,..- - ^, ....~....x4.~ 10"--^ ,^- ,')....-" i '~'.~ V ','7. \- .~'~.~---i--~ /~'~'-~ ,1971 ,\ X ', \--.. ./,' Y: '~! ~ / -~'~'-1972 :,.,~v19 7t, 10 "'>. :' -.~,' '\'1.~, ~::~1970 5" '".'%y""~Y"~ "." I : V";';v~; ~1973 u ! ! I '. ! : : : : I 2 I i " : ~- ti- 2 4 6 8 10 12 14 16 18 20 2 21, 26 28 M A M J J A g 6 bl b MONTH AGE AT 54 43 39 43 31 31 30 za 40 43 38 34 1970-74 DIAGNOSIS Fig. 1. Age variation in the incidence (annual number per Fig. 2. Seasonal variation in the diagnosis of juvenile-onset in- 100 000) of juvenile-onset insulin-dependent diabetes mellitus in sulin-dependent diabetes mellitus in Denmark in 1970-74 Denmark. (N = 474) not included in the study by the method used. These to 14. The female peak preceded the male peak by five cases are omitted from the calculations. one to two years. During early childhood the A total of 474 cases of j. i. d. m. were registered j. i. d. m. incidence gradually increased, while it re- during the five year period (Table 1). The total mained fairly stable after the age of 17-18. Smaller number of boys exceeded the number of girls by 27 peaks were present at age 7-9 and in the late twen- per cent. The calculated age-corrected incidence of ties. j. i. d. m. was found to be 13.2 per 100000 per year A seasonal variation (Fig. 2) with a reduction of (for males 14.5 and 11.9 for females) (denominator incidence during May, June and July was found. in the equation was the total number across the Geographical or familial clustering of outbreaks of whole age range involved). No major differences in j. i. d. m. was not observed in this study. age-corrected incidences between the age groups A detailed analysis of the incidence data from 0-14 and 15-29 years (Table 2) or between the the county of Copenhagen, however, showed a dif- three regions of the survey area were noted. Maxi- ference between the northern and southern part of mal year to year variation in incidence was 12.1 to the county, with most cases in the southern part. 14.3. This difference in incidence between the two areas When incidences for one year age groups were was due to a marked difference in incidence in the plotted in relation to age at diagnosis (Fig. 1), a age group 0-14 years (20.0 and 10.5 in southern marked peak incidence was demonstrated at ages 12 and northern area respectively). Table 3 demon- B. Christau et al.: Incidence of Juvenile-Onset Diabetes Mellitus 283 Table 3. Some socio-economic characteristics of the two areas of the Copenhagen county AREA I AREA II INCIDENCES OF JUVENILE DIABETES MELLITUS (ANNUAL 10.5 20.0 NUMBER PER 100000) IN THE AGE GROUPS 0--14 YEARS TH.E AGE GROUP 0-14 YEARS IN PER CENT OF THE TOTAL 23.9 27.9 POPULATION FIVE YEARS GROWTH RATE OF THE TOTAL POPULATION - 2.27 + 8.24 (IN PER CENT) THE AVERAGE NUMBER OF PERSONS PER ROOM 0,84 0.92 NUMBER OF UNSKILLED WORKERS IN PER CENT OF THE TOTAL POPULATION 9.7 13.6 NUMBER OF THE POPULATION WITH SCHOOL ATTENDANCE 7.6 3.6 ~> 11 YEARS ( IN PER CENT) NUMBER AF WOMEN WORKING AWAY FROM HOME 38.4 42.1 (IN PER CENT) PROPERTY ACCORDING TO ASSESSMENT PER FAMILY (IN DANISH CROWNS) 145,000 62.500 strates some socio-economic differences between in the summer period. Low frequency of patient- the two areas of the Copenhagen county collected doctor contacts at this time of the year). from official statistical sources. The j. i. d.m. incidence found in the present study was higher than that of the British study [1]. Obviously this might reflect true incidence differ- Discussion ences (13.2 and 7.67 respectively), but differences in degrees of ascertainment are more likely. Adams [2] described as early as 1926 a seasonal The number of males with j. i. d. m. found in this variation of "acute diabetes" with most cases occur- study was 27 per cent higher than the number of ring in fall, winter and early spring. Later Gamble females. The male excess (in numbers) in the British and Taylor [3] renewed the interest in the seasonal study can be calculated to 12 per cent. Thus sex pattern of the onset of juvenile-onset diabetes mel- seems to influence in some way the development of litus by demonstrating a seasonal variation in the j. i. d. m. In this context it is of interest that sex may age group 0-19 years similar to that described by affect the incidence of a viral infection [5] and its Adams. manifestations [6]. Also experimental diabetes can The data from the prospective study conducted be more readily produced in male than in female under the auspices of the British Diabetic Associa- animals [7] (Kromann et al. in preparation). tion [1] showed a similar seasonal pattern among The incidence of j. i. d. m. varies with age. A 2000 0-15 year old newly diagnosed diabetics.